This invention relates to polyurethane compositions which cross-link via a silane polycondensation and contain at least one alkoxysilane-functional polyurethane, at least one basic filler, at least one reaction product of an aminosilane with a maleic or fumaric ester, at least one organometallic compound and optionally additional auxiliary substances, to a process for their preparation, and to their use.
Alkoxysilane-functional polyurethanes which cross-link via a silane polycondensation are part of long-known prior art. A survey of the topic is to be found in xe2x80x9cAdhesives Agexe2x80x9d 4/1995, page 30 ff. (authors: Ta-Min Feng. B. A. Waldmann). Such alkoxysilane-terminated, moisture-curing one-component polyurethanes are increasingly being used as flexible elastic coating, sealing and adhesive compositions in the construction industry and in the automobile industry. For these applications, high demands are placed on the extensibility, the adhesive power and on the speed of cure.
Such products are described by way of example in EP-A 596360, EP-A 831108, EP-A 807649 or in EP-A 676403. Organometallic catalysts as well as adhesion promoters of the aminosilane type are commonly used concomitantly in the formulation of systems of this kind. But the addition of aminosilane compounds can often lead to problems with stability in storage, particularly when higher proportions of aminosilanes are used in order to achieve a good adhesion to difficult substrates.
Accordingly, the object of the present invention was to provide polyurethane compositions which cross-link via a silane polycondensation, contain aminosilanes and have an improved stability in storage.
This object was achieved by the provision of the polyurethane compositions which cross-link by condensation described in more detail below.
The invention provides polyurethane compositions which cross-link via a silane polycondensation, containing
A) at least one alkoxysilane-functional polyurethane having end groups corresponding to the general formula (I) 
xe2x80x83wherein
R1 represents an organic group having 1 to 12 carbon atoms,
n is an integer from 2 to 4 and
X, Y, Z denote identical or different organic groups, with the proviso that at least one of the groups is an alkoxy group having 1 to 4 carbon atoms, preferably a methoxy or ethoxy group,
B) at least one basic filler,
C) at least one reaction product of at least one aminosilane corresponding to the general formula (II) 
xe2x80x83wherein
R2 represents a hydrogen atom, or an aminoethyl group and
n, X, Y, Z have the meanings given for formula (I),
with at least one maleic or fumaric (ester) corresponding to the general formula (III)
R3OOCxe2x80x94CHxe2x95x90CHxe2x80x94COOR3xe2x80x83xe2x80x83(III),
xe2x80x83wherein
R3 represents an alkyl group having 1 to 12 carbon atoms,
E) at least one organometallic compound and
F) optionally additional auxiliary substances.
The invention is based on the surprising observation that the adducts of aminosilanes with maleic or fumaric esters which, according to the invention, are used instead of the aminosilanes conventionally employed as adhesion promoters, bring about improved mechanical properties and an improved stability in storage.
The reaction products of maleic or of fumaric esters and aminosilanes which according to the invention are to be used as component C) are known in principle and are described by way of example in EP-A 596360 or EP-A 831108. According to the disclosures in these publications, the reaction products of maleic or of fumaric esters with aminosilanes are used for the reaction with isocyanate prepolymers. The use of these products as an additive for improving the mechanical properties and for improving the adhesion of polyurethanes which cross-link via silane polycondensation is hitherto unknown.
The polyurethanes having alkoxysilane end groups which according to the invention are to be used as component A) are known in principle and are prepared by reacting long-chain, preferably linear, NCO prepolymers with aminofunctional silanes corresponding to the general structural formula (II) 
wherein R1 represents an organic group having 1 to 12 carbon atoms, preferably a phenyl group or particularly preferably a group corresponding to the general structural formula (IIb), 
wherein R4 represents an alkyl group having 1 to 4 carbon atoms. In the above structural formula, n is an integer from 2 to 4, preferably 3.
X, Y, Z in the above structural formula denote identical or different organic groups, with the proviso that at least one of the groups is an alkoxy group having 1 to 4 carbon atoms. Preferably at least one of the groups is a methoxy or ethoxy group. Particularly preferably X, Y and Z each represent a methoxy group.
Examples of suitable aminofunctional silanes producing end groups corresponding to structural formula (I) are N-methyl-3-aminopropyltrimethoxysilane. N-methyl-3-aminopropyltriethoxysilane, N-butyl-3-aminopropyltrimethoxysilane. The use of N-phenyl-3-aminopropyltrimethoxysilane is preferred. It is particularly preferable to use the aspartic esters described in EP-A 596360. which are formed through the reaction of aminosilanes corresponding to the general structural formula (II) with maleic or fumaric esters corresponding to formula (III).
NCO prepolymers which can be used for the preparation of the polyurethanes A) having alkoxysilane end groups are prepared in known per se manner by reacting polyether polyols, preferably polyether diols, with diisocyanates and have an NCO content of between 0.4 and 4%.
Compounds which can be used as basic fillers B) are precipitated or ground chalks, metal oxides, metal sulfates, metal silicates, metal hydroxides, metal carbonates and metal hydrogen carbonates. Other fillers are, for example, reinforcing and non-reinforcing fillers such as, for example, pyrogenic or precipitated silicas, carbon black or quartz powder. Both the basic fillers and the other reinforcing or non-reinforcing fillers may optionally be surface-modified. Precipitated or ground chalks and pyrogenic silicas are particularly preferably used as basic fillers B). The component B) may, of course, also be mixtures of fillers.
Compounds used as component C) are reaction products of aminosilane compounds corresponding to the general structural formula (II) 
wherein
R2, X, Y, Z and n have the meanings given above,
with maleic or fumaric (esters) corresponding to the general formula (III)
R3OOCxe2x80x94CHxe2x95x90CHxe2x80x94COOR3xe2x80x83xe2x80x83(III),
xe2x80x83wherein
R3 represents an alkyl group having 1 to 12 carbon atoms.
Examples of usable aminosilane compounds corresponding to formula (II) are 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-aminoethyl-3-amino-propyltrimethoxysilane, N-aminomethyl-3-aminopropyltriethoxysilane, 3-amino-propylmethyldiethoxysilane and N-aminoethyl-3-aminopropylmethyldimethoxysilane.
In formula (III), R3 represents a linear or branched aliphatic hydrocarbon group having at most 12 carbon atoms. Examples of suitable maleic and fumaric esters are diethyl maleate, dimethyl maleate, dibutyl maleate, dioctyl maleate, diethyl fumarate, dimethyl fumarate, dioctyl fumarate.
In the case where the products in which R2 in formula (II) denotes a hydrogen atom are used as aminosilanes, in the course of the reaction with the maleic or fumaric esters in accordance with the disclosure in EP-A 596360, aspartic esters corresponding to the general structural formula (IV) are formed 
wherein
R3, X, Y, Z and n have the meanings given for formulae (II) and (III).
In the particularly preferred case, where products in which R2 denotes an aminoethyl group are used as aminosilanes corresponding to formula (II), piperazinone derivatives corresponding to the general formula (V) 
wherein
R3, X, Y, Z and n have the meanings given for formula (IV),
are formed through a cyclocondensation reaction.
All organometallic catalysts, whichxe2x80x94as is generally knownxe2x80x94promote silane polycondensation, can be used as component E). These are in particular compounds of tin and of titanium. Preferred tin compounds are, for example, dibutyltin dilaurate, dibutyltin diacetate and dioctyltin maleate, tin(II) octoate or dibutyltin bis(acetoacetonate). Preferred titanium compounds are, for example, alkyl titanates, such as tetraisopropyl titanate, tetrabutyl titanate and chelated titanium compounds, such as ethyl diisobutylbis(acetoacetate) titanate. Dibutyltin bis(acetoacetonate) is particularly preferably used as component E).
Additives and auxiliary substances F) according to the invention which may be mentioned are drying agents, plasticisers, adhesives other than those mentioned under D), thixotropic agents, light stabilisers, pigments and protective agents, for example, fungicides.
Drying agents to be mentioned in particular are alkoxysilyl compounds, such as vinyltrimethoxysilane, methyltrimethoxysilane, i-butyltrimethoxysilane, hexadecyltrimethoxysilane. Examples of plasticisers which may be given are phthalic esters, adipic esters, alklylsulfonic esters of phenol or phosphate esters. Examples of thixotropic agents which may be vixen arc polyamides, hydrogenated products of castor oil or even polyvinyl chloride. Aminosilanes of the knows kind, epoxysilanes and/or mercaptosilanes can be used as adhesion promoters in addition to the compounds mentioned under C).
The polyurethane compositions according to the invention consist preferably of 30 to 80 wt. % of component A), 10 to 50 wt. % of component B), 0.5 to 3 wt. % of component C), 0.02 to 1 wt. % of component D) and 0 to 40 wt. % of component F).
The present invention also provides a process for the preparation of the polyurethane compositions according to the invention which cross-link by condensation. In the process according to the invention, component C) is prepared in a separate reaction vessel by reacting the aminosilanes with the maleic or fumaric esters, similarly to the disclosure in EP-A 596360, in the temperature range of 0xc2x0 C. to 100xc2x0 C. Components A), B), D) and optionally E) are mixed together, with exclusion of moisture, and component C) is then added thereto.
In a preferred embodiment of the process according to the invention, the component C) used according to the invention is produced in situ. In this procedure, components A), B), D) and optionally E), together with the maleic or fumaric esters used for the preparation of C), are mixed together, with exclusion of moisture, and the aminosilanes used according to the invention to prepare component C) are then added thereto.
The present invention also provides the use of the reaction products of aminosilanes and maleic and fumaric esters, which can be used according to the invention as component C), as an additive in polyurethane compositions which cross-link by condensation.
The present invention further provides the use of the polyurethane compositions according to the invention which cross-link by condensation as sealant, adhesive or coating material.
The polyurethane compositions according to the invention which cross-link by condensation on the one hand exhibit a rapid cure with skin formation times of between 15 and 120 minutes, but on the other hand have excellent stability in storage in the temperature range of up to 60xc2x0 C.
The cross-linked polymers exhibit improved mechanical properties, in particular an improved elongation at tear as compared with similar systems containing conventional aminosilanes. Moreover, the polyurethane compositions according to the invention are distinguished by having excellent adhesion, in particular wet adhesion, to all conceivable substrates such as, for example, metal, ceramic, plastics, stone or concrete.